This invention relates to molding resins and more specifically to molding resin compositions which provide good moldability and strong adhesive properties with a respect to a lead frame or a semiconductor chip, or the like. This invention also provides cured products having high humidity resistance in electronic components, for example semiconductor devices, after the devices are dipped into molten solder.
Recently, in the field of molding of semiconductor devices, the number of functional units on a semiconductor chip has been greatly increased, and rapid progress has been made in the high density integration of semiconductor chips.
More recently, surface mounting has become more popular. A molding material used in such devices must have a high resistance to humidity after the device has been dipped into molten solder at a high temperature (260.degree. C.) for several seconds. Conventional molding resins do not meet the current requirements for thermal resistance and thermal shock resistance on account of the high integration of the semiconductor devices. In the prior art, an epoxy resin typically was used as a molding resin for semiconductor encapsulation. In particular, epoxy resin cured with a phenol novolac resin is the most common molding resin currently in used due to its excellent humidity resistance, and its high temperature electronic characteristics and moldability.
However, this conventional epoxy resin has some problems. With this resin, cracks are often generated in a phosphorus silicate glass film (PSG) or a silicon nitride film (SiN) used to cover the surface and protect the aluminium pattern of the semiconductor element from moisture penetration, and cracks may be generated in the semiconductor chip itself. This cracking tendency frequently appears during thermal cycle test of the devices.
As a result, failures based on chip cracking or corrosion of the aluminium pattern due to cracking of the protecting film occur. Cracks often generate on the boundary between the semiconductor chip or lead frame and the molding resin after the semiconductor device is dipped into molten solder at about 260.degree. C. This causes the device to failure or operate unproperly.
To overcome the above problems, it is necessary that the stress on the inner enclosure of the molding resin is decreased and the adhesivity between lead frame and the glass film, e.g., PSG or SiN film on the surface of the element, must be increased. Also the hydrolizable halogen compounds in the cured product must be reduced and water absorption from the atmosphere must be decreased to protect against corrosion of the aluminium pattern on the surface of the semiconductor element. It is an important that the concentration of chloride is reduced and that the electric isolation efficiency is maintained at a high level even in environments high humidity or high temperature.
A modification method has been proposed in which the following elements are used for the epoxy molding resin cured by the phenol novolac resin to provide low stress. These elements include a terminated liquid rubber (disclosed in Japanese laid open application No. 57-42720), an epoxy modified butadiene copolymer (disclosed in Japanese laid open application No. 57-120), an alkyl phenol modified phenol novolac epoxy resin (disclosed in Japanese laid open application No. 59-30820), a siloxane modified phenol novolac epoxy resin (disclosed in Japanese laid open application No. 58-21417 and 58-34825), and a crosslinked organo siloxane copolymer powder (disclosed in Japanese laid open application No. 58-219218).
However, these compositions do not provide the necessary high adhesive properties for sealing the lead frame to the other elements of the device. As a result, these materials do not provide the necessary humidity protection. After the molded element is dipped in the molten solder, the humidity penetrates into the molded element. Generally, during the low stress method of making a resin composition, the viscosity of the resin added to the low stress agent increases in the molten state. As a result, many problems are generated. For example, the inner wiring of the device may change position or meet, or the arrangement way deteriorate.